Storage battery pack capacity checking method based on back voltage output DC / DC conversion

Abstract

The invention discloses a storage battery pack capacity checking method based on reverse voltage output DC / DC conversion, and the method comprises the steps: building system circuit connection, enabling each single battery in a battery string to be connected to common buses at two sides through a controllable switch array, enabling the buses at the two sides to be connected with a reverse voltage output DC / DC converter, and enabling the reverse voltage output DC / DC converter to be connected with a storage battery pack; switching array connection so as to perform discharge test between the to-be-tested fully-charged battery and the last emptied battery in turn; wherein a battery spacing switch does not need to be connected in series between the batteries during discharging between the adjacent batteries. And through shallow constant-current discharge with consistent cut-off discharge conditions, SOC change values of the single batteries are calculated and obtained, and full discharge nuclear capacity detection is carried out on part of the batteries with small change values so as to obtain the capacity state of the storage battery pack. According to the invention, the characteristic of input and output reverse polarity connection of the reverse voltage output conversion circuit is utilized, so that short circuit between series batteries during a discharge test is avoided; the system switching topology is simple, and the capacity test can be automatically and quickly carried out, so that the capacity checking frequency can be greatly increased, and the capacity state of the storage battery pack can be mastered in time.

Description

Technical Field

[0001] This invention relates to the field of DC power supply systems such as substations, and more specifically to a method for accrediting battery packs based on reverse-voltage output DC / DC conversion. Background Technology

[0002] As an important component of the DC system, the substation battery bank provides reliable DC power to signal circuits, emergency lighting circuits, relay protection devices, automatic devices, remote terminals, and inverters within the substation. It can be regarded as a backup power source for substation operation. Its function is to ensure uninterrupted power supply from the DC system in the event of AC power failure, serving as the last line of defense for the substation system's power supply.

[0003] Because substation battery banks are in standby mode for a long time, faults such as overall capacity, individual cell capacity, internal open circuits in individual cells, and electrolyte depletion cannot be detected in time. The occurrence of these problems will shorten the discharge time of the battery bank to the load when AC power is lost or the battery bank has no DC output. The substation will lose both AC and DC power at the same time, which will seriously affect the safe operation of substation equipment and may even cause the power system to collapse.

[0004] Therefore, power system regulations and energy departments have stipulated capacity testing for substation batteries, requiring regular verification charge-discharge tests to assess the performance of individual cells and battery packs, and to promptly identify and address aging batteries. Specific requirements include a full verification discharge test for newly installed valve-regulated sealed battery packs, a verification discharge test every two years, and annual verification discharge tests after four years of operation. Verification discharge is resource-intensive, with each cycle taking 10 hours, followed by a charging cycle of over 14 hours. For example, in one region, a power supply company, following regulations, conducted a battery verification charge-discharge test that lasted nearly two months, during which multiple battery aging issues were discovered.

[0005] During capacity verification experiments, the battery needs to be disconnected from the system and connected to testing instruments. Due to the large size of the load, transportation is inconvenient, operation is complex, and a significant amount of time is required. Existing technologies mostly use discharge instruments to perform discharge tests on the batteries. For example, Chinese invention patent application number 202110163597.1 determines whether the station's battery pack needs to be replaced based on the parameters collected by the discharge instrument. Chinese utility model patent publication number CN216696608U uses wireless communication to connect to the battery discharge instrument and collects and measures the voltage, internal resistance, and terminal temperature of each individual battery to determine the battery's health status.

[0006] A discharge tester simulates an external load by adding an adjustable resistor to the circuit, thus mimicking different operating conditions. During discharge, parameters such as battery voltage and current change over time. By testing these changes, performance parameters such as battery capacity and internal resistance can be calculated, and information such as battery health and lifespan prediction can be obtained. However, using a discharge tester for battery capacity testing requires converting electrical energy into heat; furthermore, replacing individual battery cells often necessitates manual wiring between the battery and the discharge tester. This method of capacity testing or verification for batteries in DC systems is wasteful of electrical energy, time-consuming, labor-intensive, and inefficient.

[0007] Because the capacity verification discharge using a discharge instrument is time-consuming, the required interval for capacity verification tests in the regulations is very long, ranging from 2 years, 1 year to half a year. In practical applications, due to the uncertainty of battery aging, such long intervals are no longer sufficient to meet the needs of controlling battery status.

[0008] Therefore, a new battery pack capacity testing device and system is needed to enable timely and efficient capacity testing of batteries. Summary of the Invention

[0009] The purpose of this invention is to provide a capacity verification method that can automatically and independently test each battery module in a DC battery pack and identify batteries with abnormal capacity.

[0010] Given the inefficiency and waste of discharge instruments in capacity testing, this invention proposes replacing the resistor with a discharged battery as the discharge load. During the design process, it was found that when discharge occurs between two battery modules, the voltage at the discharge end continuously decreases while the voltage at the receiving end continuously increases. Therefore, a DC / DC converter circuit is introduced to adjust the voltage at the receiving end.

[0011] Generally, DC / DC converters used for power supply employ non-inverting output circuits, meaning the output voltage and input voltage have the same polarity. Testing revealed that when common non-inverting output converters such as Zeta or SEPIC converters are used for battery voltage matching, topology limitations can lead to short-circuiting of some battery modules by the DC / DC converter circuit. Therefore, this invention proposes using a DC-DC converter circuit with reverse voltage output as the battery voltage matching module.

[0012] Specifically, the technical solution of the present invention is to provide a battery pack capacity assessment method based on reverse voltage output DC / DC conversion, comprising the following steps:

[0013] S1. Initialization: Charge each individual battery in the battery pack to full charge, disconnect the battery pack from the DC bus of the substation DC system, and initialize the system configuration parameters and calculation parameters.

[0014] S2. Establish system circuit connections, connect each individual battery cell to the common bus on both sides via a controllable switch array, and connect the reverse voltage output DC / DC converter to the common bus on both sides.

[0015] S3. Obtain the first empty state battery by discharging;

[0016] S4. By controlling the controllable switch, select a fully charged battery under test as the power source and a battery that has just been emptied as the load, and connect them to the input and output terminals of the reverse voltage output DC / DC converter respectively via a common bus;

[0017] S5. By adjusting the duty cycle of the PWM wave of the active switch in the reverse voltage output DC / DC converter through feedback control, the battery under test discharges to the load battery with a preset current.

[0018] S6. Based on the voltage and current parameters detected at the discharge terminal, periodically update the SOC change value of the tested battery and determine whether the discharge termination condition has been met; if so, proceed to S7, otherwise proceed to step S5.

[0019] S7. Disconnect the selected battery from the common bus and determine whether all batteries have been detected. If yes, go to S8; otherwise, go to S4.

[0020] S8. Output the SOC change value of each individual cell in the battery pack, sort them, and perform a full discharge capacity test on the first L individual cells starting from the smallest one according to the service life of the battery cells.

[0021] S9. If there is a battery with insufficient capacity, prompt the user and replace the battery.

[0022] S10. Test complete. Disconnect the controllable switches connected to the buses on both sides and restore the connection between the battery pack and the DC bus in the substation DC system.

[0023] Where L is a preset value. Preferably, step S3 can be completed before step S2.

[0024] Preferably, step S2 further includes connecting the input and output terminals of the reverse-voltage output DC / DC converter to one side and the other side of the common bus on both sides using a controllable switch in the switch array, and closing the channel between the reverse-voltage output DC / DC converter and the common bus on both sides through switching control of the control unit; the reverse-voltage output DC / DC converter is a Buck-Boost converter or a Cuk converter, etc.

[0025] Preferably, by switching control of the control unit, both ends of the DC / DC converter can be connected to the first bus and the second bus of the two common buses on both sides respectively, and the two ends of the DC / DC converter are connected to different common buses during operation; so that the fully charged battery under test and the battery that has just been discharged form a discharge working circuit with the reverse voltage output DC / DC converter through the two common buses.

[0026] Preferably, step S2 further includes, when establishing the system circuit connection, such that: each individual cell in the battery string formed by the battery pack unit has its positive and negative terminals connected to one of the pairs of wires in either the first bus or the second bus through a controllable bus switch, and adjacent cells share the middle path from the bus switch to the bus; step S4 further includes, selecting the fully charged battery under test as the individual cell whose negative terminal is adjacent to the battery that has just been emptied.

[0027] Preferably, step S2 further includes, when establishing the system circuit connection, that: the positive and negative terminals of each individual cell in the battery string formed by the battery pack unit are respectively connected to the four paths formed by the positive and negative terminals of the first bus and the second bus through a controllable bus switch, and only two of the paths are connected in series with a battery module switch connecting adjacent individual cells.

[0028] Step S4 further includes controlling the fully charged battery under test and the just-drained battery to be connected to one side of the common bus on both sides, respectively, so as to be connected to the input and output terminals of the reverse voltage output DC / DC converter.

[0029] Preferably, step S2 further includes establishing the system circuit connection such that: each individual battery cell has only one electrode in its positive and negative terminals, and before that electrode is connected to either the first bus or the second bus via a bus switch, it first passes through the same battery module switch.

[0030] Preferably, step S2 further includes, when establishing the system circuit connection, such that: for any electrode of the positive and negative terminals of the single cell, in the two paths of the first bus and the second bus respectively connected to the electrode via a bus switch, there is only one path that first passes through a battery module switch before being connected to the bus switch.

[0031] Preferably, two of the four paths that first pass through a battery module switch and then connect to the bus switch are both connected to the same bus; or, two of the paths that first pass through a battery module switch and then connect to the bus switch are each connected to one of the two buses.

[0032] Preferably, the initialization process in step S1 further includes raising the voltage of each individual cell in the battery pack to the same voltage during the pre-charging phase, and then disconnecting the individual cell when the charging current reaches the same current value during the constant voltage phase.

[0033] Preferably, during the initialization process in step S1, the connection between the two ends of the series-connected battery pack and the DC bus is disconnected. This connection can be made using a high-power active switch, and the control unit controls the on / off state of the channel connected to the switch by switching the control terminal of this high-power active switch.

[0034] Preferably, the circuit connection in step S2 is a pre-connection, that is, each independent battery module or individual battery is connected to the wires of the two common buses, namely the first bus or the second bus, via the channel controllable switch or bus switch in the controllable switch array, and / or the battery module switch, namely the battery interval switch.

[0035] Preferably, in steps S5 and S6, voltage and current parameters during discharge are collected by the voltage sensing unit and the current sensing unit, respectively; in step S6, the SOC change of the battery under test at time t is calculated.

[0036]

[0037] Preferably, the current sensing unit uses a Hall sensor to detect the discharge current on the bus connected to the discharge battery. The output signal of the Hall sensor is sent to a multiplexer after passing through a current conditioning circuit, and then converted into a digital signal by an AD converter before being sent to the control unit. The voltage sensing unit detects the potential difference between a pair of wires corresponding to the bus connected to the discharge battery. The voltage is sent to a multiplexer after passing through a voltage conditioning circuit, and then converted into a digital signal by an AD converter before being sent to the control unit.

[0038] Preferably, step S3 includes controlling the switching of the controllable switches in the switch array so that a selected single cell in the battery pack is connected to a high-power load through one of the two common buses, and controlling the discharge current of the controllable switch on the connection path between the single cell and the high-power load to a preset value, and stopping the discharge when the discharge termination condition is met.

[0039] Preferably, the preset current value is I. 10 .

[0040] Preferably, the feedback control in step S5 includes using a preset current as a current reference value, performing differential calculation with the discharge current collected by the current sensing unit, sending the differential result to the PI controller for processing as a modulation quantity, comparing it with a periodic carrier wave to generate a PWM signal, which serves as the drive signal for the active switch, i.e., the controllable switch of the converter, in the DC / DC conversion unit.

[0041] Preferably, the ratio of the output voltage to the input voltage of the reverse-voltage output DC / DC converter unit is M(D) = -D / 1-D, where the duty cycle D is adjusted by the feedback controller in the control unit according to the control law, so that the controlled current or voltage tends to be consistent with the target value and is periodically time-controlled by the digital controller according to the preset curve.

[0042] Preferably, the discharge termination condition in step S6 is that the discharge battery voltage drops to k1 times the discharge cutoff voltage, where k1 is 1.035 to 1.12 times. The discharge cutoff voltage of a 2V lead-acid single cell can be 1.8V, and the discharge cutoff voltage of a 12V battery can be 10.8V.

[0043] Preferably, when performing a 50% capacity discharge test, the discharge termination condition in step S6 is that the discharge battery voltage drops to k2 times the discharge cutoff voltage; preferably, k2 is 1.01 to 1.025 times.

[0044] Preferably, the value of L is such that, starting from the second year, the value with the smallest change in SOC is fully discharged and the core capacity is increased by one or more each year thereafter.

[0045] Preferably, step S3 is completed before or after step S2; step S8 is replaced by: performing capacity calculation and analysis, sorting the SOC change values ​​of each individual battery cell from smallest to largest, and then performing a full discharge capacity test according to the sorting results: that is, performing a full discharge capacity test on the independent battery module with the smallest SOC change value; if its capacity does not meet the requirements, then continuing to perform a full discharge capacity test on the independent battery modules ranked after it, repeating the iteration.

[0046] Preferably, in step S8, during capacity calculation and analysis, the mean and variance of all SOC changes are also calculated. When the variance is greater than a first preset variance value, the above-mentioned full-discharge capacity test is performed on each independent battery module whose deviation value (after subtracting the mean from the SOC change value) is negative and whose absolute deviation value is greater than a preset deviation value. Otherwise, the above-mentioned full-discharge capacity test based on the sorted results is performed only when the variance is less than the first preset variance value and greater than the second preset variance value. When the variance is less than the second preset variance value, only the independent battery module whose SOC change value is closest to the mean is subjected to the full-discharge capacity test, and the test result represents the overall performance of the battery pack unit. The first preset variance value is greater than the second preset variance value.

[0047] Preferably, in step S3, a selected single cell is discharged to the AC terminal through a DC / AC conversion unit as a load to obtain the first emptied cell.

[0048] Preferably, step S8 further includes displaying the SOC change value of each individual battery cell on a display screen and uploading the data to a remote server via a communication port; step S9 further includes fully charging each battery in the battery pack using an AC / DC converter unit before the test ends.

[0049] Preferably, the SOC change value is displayed in the form of a chart, preferably a bar chart, and the battery number corresponding to the minimum value is highlighted with a color different from the background.

[0050] Preferably, based on the AC / DC conversion unit, the switching control of the controllable switches in the switch array can also enable each independent battery module in the battery pack unit to obtain charging current from the first bus or the second bus.

[0051] Preferably, the AC / DC conversion unit is also controlled so that each independent battery module in the battery pack unit is charged according to a set voltage or current.

[0052] In another embodiment of the present invention, a battery pack capacity testing method based on reverse voltage output DC-DC conversion is also provided, which includes the following steps:

[0053] S1. Initialization: Charge each individual battery in the battery pack to full charge, disconnect the battery pack from the DC bus of the substation DC system, and initialize the system configuration parameters and calculation parameters.

[0054] S2. Establish system circuit connections, connect each individual battery cell to the common bus on both sides via a controllable switch array, and connect the reverse voltage output DC / DC converter to the common bus on both sides.

[0055] S3. Obtain the first empty state battery by discharging;

[0056] S4. Using a controllable switch, select a fully charged battery under test as the power source and a partially discharged battery as the load, and connect them respectively to the input and output terminals of the reverse-voltage output DC / DC converter via a common bus.

[0057] S5. By adjusting the duty cycle of the PWM wave of the active switch in the reverse voltage output DC / DC converter through feedback control, the battery under test discharges to the load battery with a preset current.

[0058] S6. Based on the voltage and current parameters detected at the discharge terminal, periodically update the SOC change value of the tested battery and determine whether the discharge termination condition has been met; if so, proceed to S7, otherwise proceed to step S5.

[0059] S7. Disconnect the selected battery from the common bus and determine whether all batteries have been detected. If yes, go to S8; otherwise, go to S4.

[0060] S8: Outputs the SOC change value of each individual cell in the battery pack;

[0061] S9. Test complete. Disconnect the controllable switches connected to the buses on both sides and restore the connection between the battery pack and the DC bus in the substation DC system.

[0062] Preferably, step S3 can be completed before step S2.

[0063] Compared with the prior art, the method of this invention has the following advantages:

[0064] This invention relates to a battery pack capacity assessment method based on reverse-voltage output DC / DC conversion. By using a variable connection of a switching array to alternately select one or two battery modules connected to two pairs of test buses, it achieves automated capacity assessment of each battery cell in a DC battery pack, eliminating the need for manual wiring when replacing the battery under test. Compared to traditional capacity assessment methods that convert battery energy into heat energy, this invention uses a DC / DC unit with step-up / step-down capability connected between the cyclically switching one or two battery modules for discharge and charge. Through the cyclic discharge between the modules within the battery pack, energy waste is avoided.

[0065] During the cyclic discharge process of each battery module, a set of SOC change values ​​for each independent battery module is obtained through shallow discharge with consistent cutoff conditions. Based on this set, analysis and calculation are performed to identify battery module numbers with significantly deviated capacity values. Combined with full-discharge capacity verification, battery modules with insufficient capacity are then identified. This invention only requires full-discharge capacity verification for individual batteries, eliminating the lengthy process of full-discharge capacity verification for all batteries, significantly saving testing time and resources. Furthermore, the automated switching of the tested battery modules and shallow discharge greatly increase the frequency of capacity verification, thereby reducing the risk of DC power supplies being affected by insufficient battery capacity.

[0066] Meanwhile, during the discharge of the selected discharge and rechargeable battery modules within the same group, this invention utilizes a combination of topology design and control via a switch array. By leveraging the characteristics of adjacent batteries being connected at their positive and negative terminals and the reverse polarity of the DC-DC converter output voltage, it avoids the short-circuit problem caused by common grounding in typical DC / DC converters. Furthermore, the topology eliminates the need for inter-battery isolation. Introducing an inter-battery separator switch further expands the flexibility of discharge and charging through various simplified topology designs. Discharge tests between batteries of similar capacity provide a more intuitive understanding of capacity differences.

[0067] This invention not only improves energy efficiency, simplifies testing, and saves testing time, but also effectively reduces the risk of insufficient battery module capacity in DC power supply systems.

[0068] It should be understood that all combinations of the foregoing concepts and the additional concepts discussed in more detail below (provided that such concepts are not inconsistent with each other) can be contemplated as part of the inventive subject matter disclosed herein. In particular, all combinations of the claimed subject matter appearing in this disclosure can be contemplated as part of the inventive subject matter disclosed herein. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to the present invention;

[0070] Figure 2 This is a schematic diagram of the component connections in a battery pack capacity system based on reverse voltage output DC-DC conversion.

[0071] Figure 3 This is a schematic diagram of a battery pack capacity integration device and a battery pack capacity integration system based on reverse voltage output DC-DC conversion.

[0072] Figure 4A This is a schematic diagram of the control unit. Figure 4BThis is a structural diagram of the loop control module and the output module;

[0073] Figure 5A , Figure 5B A schematic diagram of a topology for a switch array between rechargeable batteries;

[0074] Figure 6A , Figure 6B This is a schematic diagram of a DC / DC converter topology with the same polarity output.

[0075] Figure 7A , Figure 7B , Figure 7C , Figure 7D This is a schematic diagram showing the connection of the battery pack to the charge / discharge bus via a switch array;

[0076] Figure 8A , Figure 8B This is a schematic diagram of a reverse-voltage output DC / DC converter topology. Figure 8C The schematic diagram shows the Buck-Boost converter circuit used.

[0077] Figure 9A , Figure 9B A schematic diagram showing the connection between the DC / DC converter unit, high-power load, and bus.

[0078] Figure 10 This is a schematic diagram of current and voltage sensing data acquisition.

[0079] Figure 11 This is a schematic diagram of the PWM control principle for a DC / DC converter circuit.

[0080] In the diagram: 1000 Battery pack capacity system based on reverse voltage output DC-DC conversion, 100 Battery pack capacity device based on reverse voltage output DC-DC conversion, 200 Switch array, 300 AC / DC conversion unit, 400 High-power load, 500 Battery pack unit; 600 Bus unit, 700 Reverse voltage output DC / DC conversion unit, 800 Server.

[0081] 110 Event detection unit, 120 Voltage sensing unit, 130 Current sensing unit, 140 User interface unit, 150 Control unit;

[0082] 151 Input module, 152 Loop control module, 153 Event processing module, 154 SOC processing module, 155 PWM adjustment module, 156 PWM signal generation module, 157 Output module, 158 Storage module;

[0083] 1521 Battery switching unit, 1522 Load switching unit, 1523 External charging switching unit;

[0084] 1571 Remote linkage terminal, 1572 Communication interface terminal;

[0085] 510 is the first battery, and 520 is the second battery;

[0086] 610 first bus, 620 second bus. Detailed Implementation

[0087] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0088] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0089] The invention is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0090] Example 1:

[0091] Batteries used in substations and power plants are chemical power sources. During use, some batteries may age prematurely or fail, severely impacting the overall power supply level of the battery bank or even rendering it unable to supply power. Substation batteries play a crucial role as backup power in the power system. In the event of AC power failure or other accidents, if the battery bank malfunctions, the power supply system will face paralysis. Because individual or partial batteries inevitably age over time, the technical regulations for the operation and maintenance of DC power supply devices for power system batteries stipulate that regular verification discharge tests must be conducted to assess the capacity and performance of individual cells and the entire battery bank.

[0092] Maintaining DC batteries is a labor-intensive task, requiring significant manpower and resources. Many battery maintenance systems rely on temporarily setting up backup battery banks for on-site maintenance. While some systems utilize online discharge equipment, its low utilization rate and high cost hinder its widespread adoption. Currently, capacity testing of battery banks in power plants and substations often involves using a discharge tester to discharge battery banks temporarily disconnected from the DC bus at both ends. This method requires operators to be on-site for wiring and wastes electrical energy through resistance heating.

[0093] Therefore, such as Figure 1 As shown, this invention proposes a battery pack capacity assessment method based on reverse voltage output DC / DC conversion, which includes the following steps:

[0094] S1. Initialization: Charge each individual battery in the battery pack to full charge, disconnect the battery pack from the DC bus of the substation DC system, and initialize the system configuration parameters and calculation parameters.

[0095] S2. Establish system circuit connections, connect each individual battery cell to the common bus on both sides via a controllable switch array, and connect the reverse voltage output DC / DC converter to the common bus on both sides.

[0096] S3. Obtain the first empty state battery by discharging;

[0097] S4. Using a controllable switch, select a fully charged battery under test as the power source and a partially discharged battery as the load, and connect them respectively to the input and output terminals of the reverse-voltage output DC / DC converter via a common bus.

[0098] S5. By adjusting the duty cycle of the PWM wave of the active switch in the reverse voltage output DC / DC converter through feedback control, the battery under test discharges to the load battery with a preset current.

[0099] S6. Based on the voltage and current parameters detected at the discharge terminal, periodically update the SOC change value of the tested battery and determine whether the discharge termination condition has been met; if so, proceed to S7, otherwise proceed to step S5.

[0100] S7. Disconnect the selected battery from the common bus and determine whether all batteries have been detected. If yes, go to S8; otherwise, go to S4.

[0101] S8. Output the SOC change value of each individual cell in the battery pack, sort them, and perform a full discharge capacity test on the first L individual cells starting from the smallest one according to the service life of the battery cells.

[0102] S9. If there is a battery with insufficient capacity, prompt the user and replace the battery.

[0103] S10. Test complete. Disconnect the controllable switches connected to the buses on both sides and restore the connection between the battery pack and the DC bus in the substation DC system.

[0104] Step S3 can be completed before step S2.

[0105] refer to Figure 2 As shown, the battery pack includes BA1 to BA2. nThere are n independent battery modules, which are individual cells connected end-to-end to form a battery string. Without loss of generality, the battery strings are arranged from top to bottom, with the positive terminal of BA1 connected to the negative terminal of BA2. When performing capacity testing on the battery pack using the battery pack capacity assessment method based on reverse voltage output DC-DC conversion according to this invention, the negative terminal of BA1 is connected to the negative terminal of BA2. n The positive terminal is temporarily disconnected from the DC bus of the DC system; and through the control of the switch array, two individual batteries are selected and connected to the first bus B1 and the second bus B2 respectively. At the same time, a DC / DC converter is connected between the two buses. Through the negative feedback closed-loop control of the control unit, the first battery of the two selected batteries, i.e. the discharge battery, discharges to the second battery of the two batteries, i.e. the recharge battery, at a preset current value until the discharge termination condition is reached, such as the voltage sensor unit detecting that the voltage of the discharge battery drops to the preset discharge termination voltage.

[0106] The introduction of the DC / DC converter addresses the challenge of maintaining the current direction when a discharged battery replaces a resistor as the discharge load in the discharge circuit. During discharge between two battery modules, the voltage of the receiving battery continuously increases because the load is a battery, not a resistor; simultaneously, the voltage of the discharging battery continuously decreases as energy is transferred. To maintain the discharge current, a DC / DC converter is introduced to dynamically adjust the voltage at the discharging end (e.g., on the first bus B1) before sending it to the load via the second bus B2. Furthermore, to ensure unidirectional constant current discharge throughout the entire transition from a fully charged to a discharged state, this DC / DC converter employs a step-up / step-down mechanism.

[0107] Generally, DC / DC converters use in-phase output, meaning the output voltage and input voltage have the same polarity. This type of voltage-direction-friendly output voltage can be directly used to power the load. Inverse-output converters, on the other hand, are generally difficult to use directly as power supply circuits and usually require a second inversion or reverse voltage step before they can function as such.

[0108] However, during the design of the battery capacity test in this invention, as the testing progressed, it was discovered that when non-inverting output converters such as Zeta converters or SEPIC converters were used in this test system for voltage matching between the two batteries, some battery modules would be short-circuited by the DC / DC converter circuit due to topology limitations. Therefore, this invention proposes to use a DC-DC converter circuit with reverse voltage output as the voltage conversion and matching module for the two batteries.

[0109] Specifically, in combination Figure 2 , Figure 3As shown, the battery pack capacity assessment device 100 based on reverse-voltage output DC-DC conversion using the method of the present invention includes: a control unit 150 and a voltage sensing unit 120 and a current sensing unit 130 connected to the control unit 150. The voltage sensing unit 120 and the current sensing unit 130 are respectively used to detect the voltage and current of each independent battery module in the battery pack unit 500, sample and obtain the terminal voltage and charging / discharging current values ​​of each independent battery module (i.e., a single cell / single battery module) in the battery pack unit, and transmit them to the control unit 150 for parameter display and charging / discharging process control; and the control unit 150 is configured as follows:

[0110] By controlling the switching of the controllable switches in the switch array 200, a fully charged battery (i.e., the first battery 510) and a emptied battery (i.e., the second battery 520) in the battery pack unit 500 are respectively used as a discharge battery and a rechargeable battery. The positive and negative terminals of the discharge battery and the rechargeable battery are respectively connected to the first bus 610 and the second bus 620 in the bus unit 600 through a controllable switch in the switch array 200.

[0111] The switch array 200 integrates multiple controllable switches. The two channels of each controllable switch are respectively connected to the two modules connected to it that need to be switched. The control terminals are all connected to the output module of the control unit. Thus, the control unit can open or close the controllable switch through the corresponding output port to realize the on / off switching of the channel connected in series.

[0112] Bus unit 600 has at least two buses: a first bus 610 and a second bus 620. These two buses serve as common channels for the discharge current flowing between different independent battery modules in the battery pack unit when they are selected as discharge batteries and / or recharge batteries, respectively. To establish a common DC / DC converter unit in the discharge circuit, the DC / DC converter unit is connected between the two common buses, thus forming a discharge circuit topology under the switching control of the control unit on the controllable switch: discharge battery, discharge battery-side controllable switch or bus switch, first bus, DC / DC converter unit, second bus, charging-side controllable switch, and rechargeable battery connected in sequence. The positions of the first bus and the second bus are interchangeable.

[0113] Preferably, the battery pack capacity device 100 based on reverse voltage output DC-DC conversion can also be externally configured with a user interface unit 140 connected to the control unit. The user interface unit 140 includes a main switch, a display screen and an operation panel, which are used to input parameters and initiate operations. Human-machine interaction and other operations can be performed through the display screen and the operation panel.

[0114] Preferably, an event detection unit 110 can also be configured in the device. The event detection unit 110 is used to detect timed events and external triggers, such as periodic timed triggers for capacity detection, external charging and discharging commands, battery pack unit status refresh, etc., and then transmits the information to the input module of the control unit 150.

[0115] To ensure that electrical energy can be transferred from the discharging battery to the recharging battery regardless of whether the voltage difference between them is positive or negative, a DC / DC converter unit with buck-boost capability is selected. First, try using... Figure 6A , 5B The DC-DC converter circuits shown are the Zeta converter and the SEPIC converter, respectively.

[0116] See Figure 2 As shown, the first bus B1 and the second bus B2 serve as a common channel for the selected discharge battery and charging battery to discharge via the DC / DC converter unit, while each independent battery module Ba i (i = 1, 2, ... n) are used as discharge or recharge batteries in turn. So, how exactly is each individual cell in the battery pack connected to the two buses through the switch array?

[0117] See Figure 5A As shown, the most basic connection is to connect the positive and negative terminals of each individual battery to a pair of wires on the first bus B1 and the second bus B2 respectively through two channel controllable switches, i.e., bus switches. In this topology, taking individual batteries BA1 and BA2 as a discharge battery and a rechargeable battery respectively as a test example, since both batteries can be connected to both buses, without loss of generality, we further assume that BA1 and BA2 are connected to the first bus B1 and the second bus B2 respectively. In this case, in the switch array, the channel controllable switches on the left and upper / lower inner sides of battery BA1 are closed to connect to the first bus B1, while the channel controllable switches on the right and upper / lower inner sides of battery BA2 are closed to connect to the second bus B2. At this point, it can be proceeded as follows... Figure 5A The markings shown indicate the positive and negative reference directions; in the first bus B1, the conductors, i.e., bus L1 and L2, are the positive and negative poles, respectively, and in the second bus B2, the bus L3 and L4 are the positive and negative poles, respectively.

[0118] At this time, if the DC / DC conversion unit adopts Figure 6A The Zeta converter shown. Combined with... Figure 5A , Figure 6AAs shown, the discharge circuit formed in this test example is as follows: positive terminal of single cell BA1 → Zeta converter → positive terminal of single cell BA2 → through the battery itself to negative terminal of single cell BA2 → negative terminal of single cell BA1 → through the battery itself to positive terminal of single cell BA1. Since BA1 and BA2 are adjacent, and without loss of generality, the positive terminal of BA1 and the negative terminal of BA2 are directly connected; therefore, the positive and negative terminals of single cell BA1 are directly connected, i.e., short-circuited.

[0119] However, is it possible and how can short circuits between adjacent individual cells be avoided under the action of a Zeta converter? Figure 5A Analyze the data and try changing the positive and negative reference directions of B1 on the right, such as... Figure 5B As shown, when the controllable switches on the left and upper / lower outer (not inner) channels of the closed battery BA1 are connected to the second bus B1, it is found that this does not solve the problem, indicating that it is unrelated to the selection of positive and negative terminals. Further analysis reveals that in the battery BA string, regardless of whether two adjacent BAs are assigned to the left or right bus, the battery that is positive at the adjacent connection point after passing through the Zeta converter will inevitably be directly connected to its own negative terminal, meaning that the battery will still be short-circuited. However, if the converter is replaced with... Figure 6B The SEPIC converter shown, or other DC-DC converters with the same polarity output, will have the same problem.

[0120] To solve this short-circuit problem, a design was made as follows: Figure 7A The controllable switch connection and control switching structure shown, and Figure 8A and Figure 8B The Buck-Boost and Cuk converters, shown respectively, utilize reverse-voltage output DC-DC converter circuits in conjunction with this structure under the control of the control unit. The key aspect is that each individual cell in the battery string formed by the battery pack has its positive and negative terminals connected via a controllable bus switch to one of a pair of wires on either the first or second bus. Adjacent cells share the intermediate path through the bus switch to the bus to form a loop. Correspondingly, the reverse-voltage output DC-DC converter connected between the first and second buses has its negative input terminal Vd directly connected to the physical positive output terminal Vc. Discharge occurs between adjacent individual cells, where the common terminal of these two adjacent cells corresponds to the negative terminal of the cell that is being discharged. (See also...) Figure 7AAs shown, each of the positive and negative terminals of any single cell is connected to the left and right bus via two bus switches. Taking single cell BA2 as an example, there are a total of 4 paths from the upper and lower ends to the bus via the bus switches. The path of the upper negative terminal is shared with the positive terminal of the battery BA1 above it, and the path of the lower positive terminal is shared with the negative terminal of the battery BA3 below it.

[0121] Combination Figure 8A , 7B As shown in Figures 7C and 8C, both Buck-Boost and Cuk converters are DC / DC converters that allow the output voltage to be greater than, less than, or equal to the input voltage. The output voltage of the converter is controlled by the duty cycle of a controllable switch, such as a MOSFET or IGBT. Taking the former as an example, Buck-Boost can achieve both boost and buck conversion in the same transmission direction, has a wide voltage regulation range, and a simple topology, using only one inductor for energy storage. In the figure, switches 1 and 2 correspond to the controllable switch and diode, respectively. The diode provides a freewheeling path for the inductor when the controllable switch is open.

[0122] Figure 8C A specific non-isolated Buck-Boost converter circuit is given. In the mode where the drive signal PWM pulse for the controllable switch (Q1) is positive, Q1 is closed and conducting. The input voltage charges the inductor L1, forming a loop: positive power supply → Q1 → inductor L → negative power supply. Capacitor C, which was charged during the previous cycle's off-state, releases this energy when the switch is on in the current cycle, and the output voltage is maintained by capacitor C. In the other mode where the PWM pulse is negative, Q1 is off-state, and the inductor provides energy to the output. The loop is: positive terminal of the induced electromotive force (EMF) of inductor L → capacitor C, load (i.e., rechargeable battery Vc) → diode D → negative terminal of the induced EMF of inductor L.

[0123] Since the energy of inductor L remains constant during one switching cycle, the average voltage across the inductor corresponding to the two modes is equal to zero during one switching cycle, i.e., volt-second balance. Therefore, the ratio of the output voltage to the input voltage of the Buck-Boost converter is:

[0124] M(D) = -D / 1-D.

[0125] Where D is the duty cycle of the PWM pulse driving signal of the switching transistor Q1, and the negative sign indicates that the output voltage is out of phase with the input voltage. That is, the actual physical positive terminal of the output terminal Vc is at the lower end and is directly connected to the negative terminal of Vd, while the negative terminal of Vc is at the upper end.

[0126] To illustrate the discharge control between different individual cells in this structure, without loss of generality, we will analyze the discharge circuit using battery BA1 as the rechargeable battery (i.e., the load) and battery BA2 as the discharge battery as an example. Combined with... Figure 7A , Figure 8C As shown, the discharge circuit formed at this time is as follows: positive terminal of single cell BA2 (bus L4) → Buck-Boost converter → negative terminal of single cell BA1 (bus L2) → through the battery itself to the positive terminal of single cell BA1 (bus L1) → negative terminal and positive terminal of single cell BA2 (bus L3) → through the battery itself to the positive terminal of single cell BA2; the battery electrodes are connected to the corresponding bus via a bus switch. Observing this discharge circuit, it can be seen that it can avoid the problem of short circuit in the battery.

[0127] The input and output ports of the reverse-voltage output DC / DC converter unit can be directly connected to the first bus and the second bus. (See also...) Figure 9A As shown, preferably, the reverse-voltage output DC / DC converter unit can also be connected to the first bus and / or the second bus via controllable switches in the switch array, and the controllable switches in the channels connected to the reverse-voltage output DC / DC converter unit and the first bus and / or the second bus can be controlled to open and close by the control unit. Through this connection and control between the reverse-voltage output DC / DC converter unit and the two buses, at least one end of the reverse-voltage output DC / DC converter unit can be bypassed when the bus is used for a non-DC / DC conversion channel.

[0128] At the same time, compared to Figure 5A , Figure 7A The number of bus switches used is reduced by half, simplifying the system structure. Furthermore, because this connection structure shares the connection path between adjacent batteries, any single battery can be switched to either the first bus B1 or the second bus B2. In this case, when switching between the function of any single battery as a discharge battery or a load, the connection between the input and output terminals of the DC / DC converter and the two buses remains unchanged; instead, it is achieved by changing the connection between the battery and the bus. For example, taking single battery BA2 as an example, assuming the second bus B2 is connected to the input terminal (power supply Vd) of the reverse-voltage output DC / DC converter, then single battery BA2 is used as a discharge battery when connected to the second bus B2; conversely, when single battery BA2 is used as a load, it is connected to the first bus B1 via the bus switch. In this case, the positive and negative reference directions of the pair of wires included in each of the two buses can be as follows... Figure 7AAs shown, in the definition, wires L1 and L2 in the first bus B1 are respectively the positive and negative terminals of odd-numbered batteries, or the negative and positive terminals of even-numbered batteries; similarly, buses L3 and L4 in the second bus B2 are defined. Correspondingly, any port on each of the two input / output terminals of the DC / DC converter unit can be connected to any wire on either the first bus B1 or the second bus B2 via a path; when one end of the input / output terminal is connected to a wire on the bus via a controllable switch, the other end can also be connected to a wire on the bus via a controllable switch, or it can be directly connected.

[0129] Correspondingly, the switching of the charging and discharging function of a single battery can also be achieved by changing the connection relationship between the input and output terminals of the reverse voltage output DC / DC converter unit and the first bus B1 or the second bus B2 respectively; in this case, it is not necessary to change the bus to which the single battery is connected.

[0130] Therefore, with Figure 7A To achieve topological adaptation and enable the switching of each battery module between its different functional states of discharging and charging, the design is as follows: Figure 9B The reverse voltage output DC / DC converter unit and bus connection structure shown allow the first bus B1 and the second bus B2 to be switched as discharge or charge terminals as needed.

[0131] Preferably, the reverse-voltage output DC-DC converter can also employ a bidirectional conversion circuit to... Figure 8C For example, if both Q1 and D1 are replaced with bidirectional switches and a capacitor is added on the Vd side, a bidirectional Buck-Boost converter is formed.

[0132] By employing a bidirectional Buck-Boost converter, when discharging occurs between two adjacent individual cells, either of the two adjacent individual cells can be used as the discharging battery, while the other can be used as the load, i.e., the charging battery, without changing the connection topology.

[0133] Accordingly, when the reverse-voltage output DC / DC converter unit adopts a bidirectional DC-DC converter circuit, it can be used Figure 9A The connection topology is shown.

[0134] This invention relates to a battery pack capacity assessment device based on reverse-voltage output DC-DC conversion. It iteratively replaces the batteries serving as discharge terminals through variable connections of a switch array, using the emptied batteries as the discharge load. This not only achieves automated capacity assessment of each independent battery, eliminating manual wiring operations when replacing the tested batteries, but also avoids the waste of electrical resources caused by heat generation compared to traditional capacity assessment methods that rely on discharge instruments.

[0135] To test the capacity of each battery module, preferably, the battery under test is discharged from a fully charged state with a preset current until a discharge termination condition is reached. Preferably, the termination condition is that the voltage of the battery under test drops to a preset discharge termination voltage.

[0136] After selecting and connecting the battery under test and the object to be discharged via a switch array, in order to ensure that the discharge process proceeds according to the program, it is necessary to monitor the operating current and voltage of the power supply and load at both ends of the DC / DC converter unit (which acts as the reverse voltage output) in real time during the discharge process. (See also...) Figure 10 As shown, the operating current can be detected by the Hall sensor in the current sensing unit. The Hall sensor does not need to be connected in series with the operating circuit, so it will not interfere with the operating current.

[0137] Preferably, the current detection point is set at the power supply end. In order to reduce the number of sensors, simplify the topology and reduce costs, the Hall sensor is set on two common buses, and the current value collected from the bus connected to the discharge battery end is used as the discharge current feedback value.

[0138] Preferably, the Hall sensor output signal is sent to a multiplexer after passing through a current conditioning circuit, and then converted into a digital signal by an AD converter before being sent to the control unit.

[0139] Combination Figure 7C , Figure 10 , Figure 10 Figure 11 As shown, without loss of generality, taking the control of the reverse-voltage output DC / DC converter unit using a Buck-Boost converter during discharge as an example, the real-time current at the discharge battery terminal is collected by the current sensing unit as the discharge current feedback value; and the preset discharge current value, i.e., the current reference value i, is used as the current. ref The current feedback value is differentially divided and sent to the PI controller. The PI controller obtains a control quantity through proportional-integral control, which is used as the modulation quantity. This quantity is compared with a periodic carrier wave in the PWM signal generation module to generate a PWM signal, which serves as the drive signal for the controllable switch Q1 in the Buck-Boost converter. Through this negative feedback control, the actual discharge current approaches the preset current.

[0140] Preferably, the current sensing value at the discharge battery terminal is collected and then filtered by H(s) to obtain its average current value. In a continuous system, it can be converted into a voltage value after passing through a resistor, and the current value of the reference value is also converted into a voltage value. In a discrete system, the current value is sampled multiple times during the PWM control cycle and then filtered by software to obtain its average value.

[0141] Preferably, the preset discharge current value can be taken as I of the independent battery module. 10It can also be adjusted according to the battery's service life. For example, for battery cells that have been in service for less than two years, it can be calculated as k*I. 10 Discharge is performed, where k can be taken as 1.2 to 1.5, and the coefficient k is gradually reduced as the service time increases.

[0142] See Figure 10 As shown, a voltage sensing unit is also used to detect the terminal voltage Vd across the discharge battery. Similarly, to simplify the circuit and reduce size and cost, the voltage sensing unit can detect the potential difference between a pair of buses or wires connected to the discharge battery via a voltage divider circuit. This signal is then sent to a multiplexer via a voltage conditioning circuit, converted into a digital signal by an AD converter, and finally sent to the control unit.

[0143] Preferably, the current conditioning circuit and voltage conditioning circuit include a signal amplifier circuit and a filter circuit, and may also include an isolation circuit to improve anti-interference capability and signal acquisition accuracy.

[0144] Preferably, the voltage sensing unit and the current sensing unit also collect the charging current and charging voltage of the rechargeable battery, convert them into digital signals, and transmit them to the control unit so that the control unit can perform discharge control according to the charging constraints.

[0145] During each discharge control process, the control unit collects electrical parameters during the discharge period through the voltage sensing unit and the current sensing unit, and calculates the SOC change value of the discharged battery. The SOC change value is used to measure the discharge amount of each independent battery module from the fully charged state to the empty state, thereby calculating its discharge capacity and realizing the purpose of battery pack capacity verification.

[0146] SOC, or State of Charge, reflects the remaining capacity of a battery. It is numerically defined as the ratio of remaining capacity to the total battery capacity, and is usually expressed as a percentage.

[0147] SOC = C now / C r .

[0148] The SOC value ranges from 0 to 1. SOC = 0 indicates the battery is fully discharged, and SOC = 1 indicates the battery is fully charged. Starting from the initial state, the SOC at time t is:

[0149]

[0150] To verify the usable capacity of a DC battery pack, the key lies in detecting the discharge capability of each battery module. Therefore, this invention uses sensor sampling to calculate and obtain the SOC change value during the discharge test.

[0151] Preferably, for an independent battery module used as a discharge battery, the formula for calculating the SOC change at time t is:

[0152]

[0153] To obtain the SOC change values ​​of all independent battery modules in a DC battery pack under the same test conditions, batteries for discharging and charging are cyclically selected, and the circuit connections of the selected batteries are controlled by a switch array. During this process, a fully discharged battery is used as a charging battery, and the next fully charged battery to be tested is selected as the discharging battery. Discharging tests between discharging and charging batteries are performed cyclically within the battery pack unit. The SOC change values ​​of each independent battery module in the battery pack unit are obtained by acquiring and calculating electrical parameters. Then, the SOC change values ​​of each independent battery module are analyzed and calculated, and the results are output, identifying the numbers of independent battery modules whose SOC change values ​​exceed the preset range.

[0154] As a preferred approach, the SOC change values ​​of each independent battery module are sorted during the analysis and calculation, and the first L batteries are subjected to full discharge capacity testing based on their service life, starting with the one with the smallest SOC change value. For example, starting from the second year, the battery with the smallest SOC change value is subjected to full discharge capacity testing, and then the value is increased by one each year thereafter.

[0155] As a preferred approach, the SOC change values ​​of each independent battery module are sorted from smallest to largest during the analysis and calculation. Then, a full discharge capacity test is performed based on the sorting results: that is, the independent battery module with the smallest SOC change value is subjected to a full discharge capacity test; if its capacity does not meet the requirements, the full discharge capacity test is performed on the next ranked independent battery module, and the process is repeated iteratively. All independent battery modules that do not meet the capacity requirements are output with numbers, prompting for battery replacement.

[0156] Preferably, during full discharge capacity testing, the discharge cutoff voltage for a 2V lead-acid cell is 1.8V, and for a 12V cell it is 10.8V. Preferably, for consistent shallow discharge, the discharge termination condition is that the battery voltage drops to k1 times the discharge cutoff voltage; preferably, k1 is between 1.035 and 1.12 times. Actual test experiments show that when this cutoff voltage is used, the cell discharge time is shortened from 10 hours (corresponding to 0.1C or I10) to 2-8 hours.

[0157] If the battery is discharged to 50% capacity, the discharge cutoff voltage for a single cell can be 2V. Preferably, for a more consistent and shallower discharge, the discharge termination condition is that the battery voltage drops to k² times the discharge cutoff voltage of the 50% capacity discharge; preferably, k² is between 1.01 and 1.025 times. Actual testing shows that when this cutoff voltage is used, the single-cell discharge time will be further shortened to approximately 1-2 hours.

[0158] This invention employs a method combining short-time discharge and full verification discharge tests, which significantly shortens the capacity testing time. Specifically, by analyzing and calculating the SOC changes of each individual cell, only a few cells need to undergo full discharge capacity verification, eliminating the lengthy process required for full discharge capacity verification of all cells, thus significantly saving testing time and resources. Figure 3 , Figure 9A As shown, to obtain the first discharged battery state, preferably, by controlling the switching of the controllable switches in the switch array 200, a selected independent battery module in the battery pack unit 500 is connected to a high-power load via the first bus 610 or the second bus 620. The discharge current of this path is set to a preset value by PWM control of the controllable switch on the connection path between the independent battery module and the high-power load 400, and discharge stops when the discharge termination condition is met. The high-power load is preferably a variable resistance load; alternatively, a controllable electronic load can be used, in which case the control unit communicates with it via a communication interface to adjust the load impedance and keep the current constant or varying according to a preset curve.

[0159] Since the discharge of the battery via reverse voltage output DC / DC conversion and discharge via a high-power load are two mutually exclusive operating states, it is preferable to connect the reverse voltage output DC / DC conversion unit and the high-power load in series on the same bus through two sets of mutually exclusive contact pairs of a switch.

[0160] Combination Figure 2 , Figure 3 As shown, preferably, the control unit also controls an AC power supply switch to disconnect or connect the power supply from an AC / DC converter unit to the first bus or the second bus.

[0161] Preferably, the control unit controls the switching of controllable switches in the switch array so that each independent battery module in the battery pack unit receives charging current from the first bus or the second bus.

[0162] Preferably, the control unit also controls the AC / DC conversion unit so that each independent battery module in the battery pack unit is charged according to a set voltage or current.

[0163] This invention controls the connection of adjacent individual cells within a battery string using a switch array. Through reverse-voltage DC-DC conversion, each independent battery module sequentially discharges the empty cells in the row above it, obtaining the State of Charge (SOC) change value and thus updating the battery pack's capacity status. The method combining short-time discharge and full-verification discharge tests significantly shortens the capacity verification test time. Furthermore, by analyzing and calculating the SOC change values ​​of each independent battery module, only individual cells need to undergo full-discharge capacity verification, eliminating the lengthy process required for full-discharge verification of all cells, thus saving testing time and resources.

[0164] Example 2:

[0165] In another embodiment of the present invention, a method for controllable connection switching of battery strings in a battery pack is also provided, and based on the method, discharge and charge can be achieved between batteries with similar capacities.

[0166] Specifically, based on Example 1, to improve the flexibility of the discharge circuit construction, the following design is made: Figure 7B The diagram shows the connection circuit between the battery pack and the switch array. Unlike the previous embodiment, this solution introduces a controllable inter-cell channel switch, i.e., an inter-module switch / battery spacer switch (KBA), between the individual cells in the battery string. Its characteristic is that for each individual cell in the battery string, one electrode of its positive and negative terminals is connected via a controllable bus switch to one of a pair of wires on either the first or second bus. The other electrode is then connected via a battery spacer switch and then via another bus switch to the other wire in that pair. Alternatively, for each individual cell in the battery string, its positive and negative terminals are directly connected, via a battery spacer switch and then via a bus switch, to different wires on either the first or second bus; its positive and negative terminals are also directly connected, via the same battery spacer switch and then via another bus switch to different wires on another bus.

[0167] Compared to Figure 7A , Figure 7B The circuit structure allows for cross-cell discharge circuits. For example, let's analyze the discharge circuit using battery BA1 as the rechargeable battery (load) and battery BA3 as the discharge battery. (Combined with...) Figure 7B , Figure 8CAs shown, in the discharge circuit formed at this time, although the positive terminal of cell BA1 is directly connected to the negative terminal of cell BA3 within the Buck-Boost converter, the battery separator switch KBA between cells BA2 and BA3 can be disconnected by controlling the switch array through the control unit, thus avoiding any impact on other cells and avoiding the short circuit problem. The advantage of this topology is that discharge-charge tests can be performed between any two cells, which greatly improves the flexibility of testing and the freedom of cell construction.

[0168] After obtaining the first empty battery, during the operation of the battery pack capacity assessment device based on reverse voltage output DC-DC conversion, the SOC state of each individual battery module is recorded through cyclic discharge. At the start of a new round of testing, the individual with the largest SOC change value in the previous test can be selected for discharge to obtain the first empty battery.

[0169] Preferably, based on the battery string connection topology of this embodiment, in a new round of testing, two individual batteries with similar SOC change values ​​can be selected as discharge and recharge batteries respectively for discharge testing. That is, a battery module with a SOC change value close to that of the battery in the empty state is selected as the discharge battery for discharge capacity testing.

[0170] By discharging batteries with similar capacities, the operating conditions of each battery discharge can be made more similar, making the comparison of SOC changes more intuitive to reflect the capacity differences between individual battery modules.

[0171] By conducting a battery discharge test with a gradually decreasing SOC value, the battery will be completely discharged in the later stages. This eliminates the need to change the wiring and use a high-power load to supplement the discharge during the capacity test, thus saving operations and further improving test efficiency.

[0172] Preferably, in a round of capacity testing of the DC battery bank, the first independent battery module in a discharged state obtained from an external high-power load is tested again after all other independent battery modules have completed their discharge capacity testing. This second discharge process replaces the accumulated discharge during the initial discharge period as its SOC change value. Finally, before switching the DC battery bank to the substation DC bus, the independent battery modules are fully charged via an AC / DC converter, and the connection between the first and second buses is disconnected.

[0173] Example 3:

[0174] This embodiment provides another connection structure between individual cells in a battery string and between them and two common buses to further improve the flexibility of capacity testing.

[0175] During the test, it was found that, Figure 7A , Figure 7B In the topology scheme shown, when discharge occurs between two adjacent single cells, the single cell whose common terminal of the two adjacent single cells corresponds to the negative electrode must be used as the discharge battery. That is, the discharge between adjacent cells is unidirectional, and the direction is determined by the series connection direction of the positive and negative electrodes.

[0176] Therefore, the following were designed: Figure 7C The novel connection structure and method are shown. The feature is that each individual cell in the battery string formed by the battery pack has its positive and negative electrodes connected to a pair of wires on either of the two buses via a bus switch, and then connected to a pair of wires on the other bus via at least one battery module switch. Alternatively, the positive electrode of each individual cell is directly connected to one of the pairs of wires on either the first or second bus via a bus switch, and then connected to one of the wires on the other bus via a battery spacer switch; and the negative electrode is directly connected to the other wire on the other bus via a bus switch, and then connected to the other wire on the other bus via a battery spacer switch.

[0177] Taking Example 1, with battery BA1 as the load and battery BA2 as the discharge battery, as an example, we will analyze the discharge task, combining... Figure 7C and Figure 8C As shown, a discharge circuit can be formed by controlling the switch array, where battery BA1 is connected to the second bus B2, battery BA2 is connected to the first bus B1, and the switch between the battery modules is simultaneously disconnected. At this time, by controlling the Buck-Boost converter input to connect to the first bus B1 or the second bus B2, battery BA2 can switch between functioning as a discharge battery and as a load. In comparison, Figure 7A , Figure 7B Under the current connection structure, only battery BA1 can be selected as the load and battery BA2 as the discharge battery when the discharge task is performed. However, due to the positional characteristics of the battery module switch, i.e., the battery interval switch, this embodiment can perform bidirectional discharge, further expanding the degree of freedom in capacity testing.

[0178] At the same time, it also designed such as Figure 7D Another novel connection structure and method is shown. Its characteristic is that each individual cell in the battery string formed by the battery pack has its positive and negative electrodes connected, respectively, to one wire of any one of the two bus lines via a bus switch, and then connected to the other wire of that bus line pair via a battery spacer switch; simultaneously, its negative and positive electrodes are also connected, respectively, to one wire of another bus line pair via a bus switch, and then connected to the other wire of that other bus line pair via a battery spacer switch.

[0179] because Figure 7C , Figure 7D The different connection structures result in different connections between individual battery cells and the buses on both sides when performing the same discharge test between adjacent batteries. Figure 7C Specifically, when discharging between batteries BA1 and BA2, or between batteries BA2 and BA3, battery BA2 is connected to the left bus B1, while the area between BA1 and BA3 is connected to the right bus B2. And for... Figure 7D Specifically, when discharging between batteries BA1 and BA2, battery BA2 is connected to the right bus B2; while when discharging between batteries BA2 and BA3, battery BA2 is connected to the left bus B1.

[0180] Different from Figure 7A The plan, Figure 7B , Figure 7C , Figure 7D All three topologies share a common connection characteristic: the positive and negative terminals of each individual cell in the battery string are connected to four wires in two buses via a bus switch, and only two of these buses also have an inter-module switch connected in series. Figure 7C , Figure 7D Both of these topologies share the following common feature: a battery module switch is connected in series between the connection points of the two adjacent electrodes of adjacent batteries in the battery string and the bus switch.

[0181] Example 4:

[0182] In another embodiment of the present invention, a battery pack capacity testing method based on reverse voltage output DC-DC conversion is also provided, which includes the following steps:

[0183] S1. Initialization: Charge each individual battery in the battery pack to full charge, disconnect the battery pack from the DC bus of the substation DC system, and initialize the system configuration parameters and calculation parameters.

[0184] S2. Establish system circuit connections, connect each individual battery cell to the common bus on both sides via a controllable switch array, and connect the reverse voltage output DC / DC converter to the common bus on both sides.

[0185] S3. Obtain the first empty state battery by discharging;

[0186] S4. Using a controllable switch, select a fully charged battery under test as the power source and a partially discharged battery as the load, and connect them respectively to the input and output terminals of the reverse-voltage output DC / DC converter via a common bus.

[0187] S5. By adjusting the duty cycle of the PWM wave of the active switch in the reverse voltage output DC / DC converter through feedback control, the battery under test discharges to the load battery with a preset current.

[0188] S6. Based on the voltage and current parameters detected at the discharge terminal, periodically update the SOC change value of the tested battery and determine whether the discharge termination condition has been met; if so, proceed to S7, otherwise proceed to step S5.

[0189] S7. Disconnect the selected battery from the common bus and determine whether all batteries have been detected. If yes, go to S8; otherwise, go to S4.

[0190] S8: Outputs the SOC change value of each individual cell in the battery pack;

[0191] S9. Test complete. Disconnect the controllable switches connected to the buses on both sides and restore the connection between the battery pack and the DC bus in the substation DC system.

[0192] Step S3 can be completed before step S2.

[0193] Combination Figure 10 , Figure 2 As shown, a battery pack capacity system 1000 based on reverse voltage output DC-DC conversion using the method of the present invention includes:

[0194] The battery pack unit 500 provides DC power to the outside, the switch array 200 provides variable connection between unit modules, the bus unit 600 provides a common connection path, and a DC / DC converter unit 700 is connected to the bus unit 600 at both ends.

[0195] In addition, a voltage sensing unit 120 and a current sensing unit 130 are used to detect the voltage and current of each independent battery module in the battery pack unit 500, and a control unit 150 is connected to the switch array 200, the DC / DC conversion unit 700, the event detection unit 110, the voltage sensing unit 120, the current sensing unit 130, and the user interface unit 140.

[0196] The control unit 150 is configured to control the switching of the channel controllable switches in the switch array 200, so that a fully charged battery and a emptied battery selected in the battery pack unit 500 are respectively used as a discharge battery and a rechargeable battery, and the discharge battery and rechargeable battery are respectively connected to the first bus 610 and the second bus 620 in the bus unit 600.

[0197] The DC / DC converter unit 700 is controlled to cause the discharge battery to discharge to the rechargeable battery at a preset current until the discharge termination condition is reached. The voltage sensing unit 120 and the current sensing unit 130 collect electrical parameters during the discharge process and calculate the SOC change value of the discharge battery.

[0198] Using the fully discharged battery as the rechargeable battery, and selecting a fully charged battery to be tested as the discharge battery, the discharge test between the discharge battery and the rechargeable battery is performed cyclically in the battery pack unit. The SOC change value of each independent battery module in the battery pack unit is obtained as the discharge battery by collecting and calculating electrical parameters.

[0199] The system analyzes and calculates the SOC change value of each independent battery module and outputs the results, providing the numbers of independent battery modules whose SOC change value exceeds the preset range.

[0200] Preferably, the battery pack capacity system 1000 based on reverse voltage output DC-DC conversion can also be configured with a user interface unit 140 connected to the control unit. The user interface unit 140 includes a main switch, a display screen and an operation panel, which are used to input parameters and initiate operations. Human-machine interaction and other operations can be performed through the display screen and the operation panel.

[0201] Preferably, the system can also be equipped with an event detection unit 110 to detect timed events and externally triggered events, and to provide feedback to the control unit.

[0202] Preferably, the bus unit 600 includes at least a first bus 610 and a second bus 620. When more buses are used, such as four buses, discharge circuits can be constructed between each pair, thereby further improving the efficiency of the core capacity test.

[0203] See Figure 4A As shown, preferably, the control unit 150 may include an input module 151, a loop control module 152, an event processing module 153, a SOC calculation module 154, a PWM adjustment module 155, a PWM signal generation module 156, a storage module 158, and an output module 157.

[0204] The input module 151 and output module 157 are used for signal input and output, respectively. The loop control module 152 is used for switching control of bus channel controllable switches and battery channel controllable switches in the switch array. The event processing module 153 is used for responding to external events and judging discharge termination conditions. The SOC calculation module 154 is used to calculate and analyze the SOC change value of each discharge battery during discharge based on the electrical parameters collected by the voltage sensing unit and current sensing unit. The PWM adjustment module 155 performs negative feedback control based on the collected electrical signals to make the discharge loop voltage and current track their respective target reference values ​​and send adjustment signals to the PWM signal generation module 156. The PWM signal generation module 156 generates PWM pulse signals based on the adjustment signals sent by the PWM adjustment module 155 to open or close the controllable switches of the converter in the DC / DC conversion unit 700. The storage module 158 is used to store and transfer data of the control unit during signal processing.

[0205] Preferably, the battery pack capacity system based on reverse voltage output DC-DC conversion also includes a high-power load for discharging.

[0206] See Figure 4B As shown, preferably, the output module 157 includes a remote linkage terminal 1571 for remotely triggering the dry contact of the substation operating terminal, and a communication interface terminal 1572 for transmitting signals with external devices.

[0207] Preferably, the loop control module 152 further includes a battery switching unit 1521 that controls the connection topology between the battery unit and the common bus, and between the independent modules within the battery unit; a load switching unit 1522 that controls the connection between the high-power load and the common bus; and an external charging switching unit 1523 that controls the external power supply to charge the battery unit.

[0208] Preferably, the results and intermediate data obtained from each capacity test can be stored in server 200, wherein server 200 can communicate with one or more systems of the present invention through a cloud platform and provide information interaction services for remote distributed clients.

[0209] See Figure 2 , Figure 3 As shown, preferably, the battery pack capacity system 1000 based on reverse voltage output DC-DC conversion also includes an AC / DC converter unit 300. The control unit 150 also controls the power switch in the AC / DC converter unit 300, causing each independent battery module in the battery pack unit 500 to be charged according to a set voltage or current. During the capacity test initialization process, the independent battery modules can be fully charged through the AC / DC converter unit, and then their output terminals can be disconnected from the first and second buses.

[0210] Preferably, the high-power load is replaced by a DC / AC converter unit, and under the control of the control unit, during the initial test, a selected battery module is discharged to the AC terminal through the DC / AC converter unit to obtain the first empty battery state.

[0211] Example 5:

[0212] This embodiment provides another method for analyzing and determining battery pack capacity.

[0213] Unlike the previous embodiment, the control unit also calculates the mean and variance of all SOC changes in the above analysis and calculation. When the variance is greater than a first preset variance value, the full discharge capacity test is performed on each independent battery module whose deviation value (after subtracting the mean from the SOC change value) is negative and whose absolute deviation value is greater than a preset deviation value. Otherwise, the full discharge capacity test is performed on each module individually according to the sorted results only when the variance is less than the first preset variance value and greater than the second preset variance value. When the variance is less than the second preset variance value, the full discharge capacity test is performed only on the independent battery module whose SOC change value is closest to the mean, and the test result represents the overall performance of the battery pack. The first preset variance value is greater than the second preset variance value.

[0214] The mean value of the SOC change is:

[0215]

[0216] The variance of the change in SOC is:

[0217]

[0218] The deviation of the SOC change value of the i-th individual cell is:

[0219]

[0220] The preset deviation value is set based on the experimental statistical values, and can be preferably set to 2 times the standard deviation. The first preset variance value and the second preset variance value can also be set based on the experimental statistical values, and can be taken between 3 and 8 times the standard deviation.

[0221] This embodiment further reduces the number of batteries required for full discharge capacity verification by statistically calculating and classifying the SOC changes of each independent battery module in the DC battery pack, shortening the testing time, which is beneficial for shortening the overall capacity verification test cycle and improving the real-time monitoring of battery pack capacity.

[0222] This invention relates to a battery pack capacity assessment system based on reverse-voltage output DC / DC conversion. By switching the connections between individual battery cells within the battery pack using a switch array, each individual battery can be tested for capacity through discharge. During testing, energy is not consumed through heat generation; instead, it is used to recharge the discharged batteries, thus avoiding energy waste. The switch array automatically tests each individual battery in turn, replacing manual replacement of the battery under test with automated switching. By sharing a reverse-voltage output DC / DC converter circuit, the composition of the capacity assessment device is simplified, reducing system complexity. Furthermore, through topology design and switch control, the reverse polarity connection of the input and output of the reverse-voltage output DC / DC converter circuit and the opposite polarity of adjacent electrodes in the battery string are cleverly utilized to avoid short-circuit problems through the discharge loop between adjacent individual cells within the battery string.

[0223] Based on the same capacity test conditions, partial discharge can be used to replace full discharge capacity test. By combining it with the complete verification discharge test of a few independent batteries with lagging capacity, the overall capacity of the DC battery pack can be obtained, which greatly shortens the time required for the overall capacity test of the battery pack. This allows for an increase in the frequency of capacity test, timely acquisition of changes in battery pack capacity, and helps to improve power supply reliability.

[0224] The foregoing has described several embodiments of the present invention, but these embodiments are merely illustrative examples and do not limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, combinations, and modifications can be made without departing from the spirit of the invention. These embodiments or their variations are included within the scope or spirit of the invention, and are similarly included within the scope of the invention as described in the claims and its equivalents.

Claims

1. A battery pack capacity assessment method based on reverse-voltage output DC / DC conversion, comprising the following steps: S1. Initialization: Charge each individual battery in the battery pack to full charge, then disconnect the battery pack from the DC bus of the substation DC system, and initialize the system configuration parameters and calculation parameters. S2. Establish system circuit connections, connect each individual battery cell to the common bus on both sides via a controllable switch array, and connect the reverse voltage output DC / DC converter to the common bus on both sides. S3. Obtain the first empty state battery by discharging; S4. By controlling the controllable switch, select a fully charged battery under test as the power source and a battery that has just been emptied as the load, and connect them to the input and output terminals of the reverse voltage output DC / DC converter respectively via a common bus; S5. By adjusting the duty cycle of the PWM wave of the active switch in the reverse voltage output DC / DC converter through feedback control, the battery under test discharges to the load battery with a preset current. S6. Based on the voltage and current parameters detected at the discharge terminal, periodically update the SOC change value of the tested battery and determine whether the discharge termination condition has been met. If yes, proceed to step S7; otherwise, proceed to step S5. S7. Disconnect the selected battery from the common bus and determine whether all batteries have been detected. If yes, go to S8; otherwise, go to S4. S8. Output the SOC change value of each individual cell in the battery pack, sort them, and perform a full discharge capacity test on the first L individual cells starting from the smallest one according to the service life of the battery cells. S9. If there is a battery with insufficient capacity, prompt the user and replace the battery. S10. Test complete. Disconnect the controllable switches connected to the buses on both sides and restore the connection between the battery pack and the DC bus in the substation DC system.

2. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to claim 1, characterized in that, Step S2 further includes connecting the input and output terminals of the reverse-voltage output DC / DC converter to one side and the other side of the common bus on both sides using a controllable switch in the switch array, and closing the channel between the reverse-voltage output DC / DC converter and the common bus on both sides through the switching control of the control unit. The reverse voltage output DC / DC converter adopts a Buck-Boost converter or a Cuk converter, etc.

3. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to claim 1, characterized in that, Step S2 further includes, when establishing the system circuit connection, such that: each individual cell in the battery string formed by the battery pack unit has its positive and negative terminals connected to one of the pairs of wires in either the first bus or the second bus through a controllable bus switch, and adjacent cells share the middle path from the bus switch to the bus. Step S4 further includes selecting a fully charged battery to be tested as a single cell whose negative electrode is adjacent to the battery that has just been emptied.

4. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to claim 1, characterized in that, Step S2 further includes, when establishing the system circuit connection, such that: the positive and negative terminals of each individual cell in the battery string formed by the battery pack unit are respectively connected to the four paths formed by the positive and negative terminals of the first bus and the second bus through a controllable bus switch, and only two of the paths are connected in series with a battery module switch connecting adjacent individual cells. Step S4 further includes controlling the fully charged battery under test and the just-drained battery to be connected to one side of the common bus on both sides by means of a controllable switch.

5. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to any one of claims 1 to 4, characterized in that, The initialization process in step S1 also includes raising the voltage of each individual cell in the battery pack to the same voltage during the pre-charging phase, and then disconnecting the individual cell when the charging current reaches the same current value during the constant voltage phase.

6. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to any one of claims 1 to 4, characterized in that, In steps S5 and S6, voltage and current parameters during the discharge period are collected by the voltage sensing unit and the current sensing unit, respectively. In step S6, the SOC change of the battery under test at time t is calculated:

7. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to any one of claims 1 to 4, characterized in that, Step S3 includes controlling the switching of the controllable switches in the switch array so that a selected single cell in the battery pack is connected to a high-power load through one of the two common buses, and controlling the discharge current of the controllable switch on the connection path between the single cell and the high-power load to a preset value, and stopping the discharge when the discharge termination condition is met.

8. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to any one of claims 1 to 7, characterized in that, The feedback control in step S5 includes using a preset current as a current reference value, performing differential calculation with the discharge current collected by the current sensing unit, sending the differential result to the PI controller for processing as a modulation quantity, comparing it with a periodic carrier wave to generate a PWM signal, which serves as the drive signal for the active switch in the DC / DC converter unit.

9. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to any one of claims 1 to 8, characterized in that, Step S3 is completed before or after step S2; Step S8 is replaced by: performing capacity calculation and analysis, sorting the SOC change values ​​of each individual battery cell from smallest to largest, and then performing a full discharge capacity test according to the sorting results: that is, performing a full discharge capacity test on the independent battery module with the smallest SOC change value; if its capacity does not meet the requirements, then continuing to perform a full discharge capacity test on the independent battery modules ranked after it, repeating the iteration.

10. The battery pack capacity assessment method based on reverse voltage output DC / DC conversion according to claim 9, characterized in that, In step S8, during capacity calculation and analysis, the mean and variance of all SOC changes are also calculated. When the variance is greater than a first preset variance value, the above-mentioned full-discharge capacity test is performed on each independent battery module whose deviation value (after subtracting the mean from the SOC change value) is negative and whose absolute deviation value is greater than a preset deviation value. Otherwise, the above-mentioned full-discharge capacity test based on the sorted results is performed only when the variance is less than the first preset variance value and greater than the second preset variance value. When the variance is less than the second preset variance value, only the independent battery module whose SOC change value is closest to the mean is subjected to the full-discharge capacity test, and the test result represents the overall performance of the battery pack unit. The first preset variance value is greater than the second preset variance value.

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